In order to ensure that visual images are properly displayed, systems have been developed to determine that the image and the visual display device onto which the image is projected are properly aligned. Proper alignment requires the comparison of reference points located or projected onto the viewing surface of the display device with similar points in an appropriate test pattern.
Previously known systems use modified slide projectors or slide projectors incorporating custom lenses and specially designed optical reticles. Alignment is achieved using either a laser theodolite or a removable clear plastic overlay template. Such a template may be installed on the face of a CRT, for example. The laser theodolite and the template may be used in conjunction to achieve the desired alignment of image and visual display device.
These previously known systems suffer from both installation and manufacturing tolerance problems. For example, back projections screens are free form blow molded. The curvature of screens produced by this process may vary from screen to screen. As a result of this variation in curvature resulting from the fabrication process, optical reticles may yield variations in tolerances from screen to screen during the alignment process.
Repeated attachments of the above-mentioned templates may lead to installation tolerance problems where the actual orientation of the template relative to the display device may vary slightly from one application to the next. As a result, attempts to evaluate alignment of image and the display device may lead to variations in tolerance when evaluations are repeated over a period of time.
The use of laser theodolites may prove expensive and very time-consuming to use in aligning images with visual display devices. Using a laser theodolite, which resembles the device used by surveyors to measure angles, the reference points are mapped on the viewing surface of the display device. The locations of the various reference points are given as coordinates, usually azimuth and elevation. However, when using a laser theodolite, each reference point must be mapped individually. Therefore, deviations from proper alignment are determined only when the map of reference points is completely constructed and the resulting map of reference points is compared with the test pattern.
Accordingly, corrections to the alignment of the display device and the test pattern due to orientation problems or distortion of the image can be made only after reconstruction of the entire array of reference points. Therefore, the use of laser theodolites is very time-consuming and expensive when determining whether an image is properly aligned with the visual display device.
The present invention addresses the above-mentioned problems in the previously known systems to provide a method and apparatus for efficiently aligning an image and a display device.